1. Field of the Invention
This invention relates to an oil pressure type pneumatic torque wrench and has for its object to generate stabilized high torque, without raising much the oil pressure in an oil pressure type impulse torque generator, by producing one impact at each rotation of a liner with the use of two blades.
2. Prior art
Prior pneumatic torque wrenches generate impact by a mechanical method based on the turning power of a rotor and such impact is converted into the desired torque. Therefore, in this system of obtaining impacting torque by a mechanical method, as the torque of one impact is large, an irregular tightening torque is liable to take place and accordingly skill is required for tightening with uniform torque. Also, the impact noise is high, which can cause noise pollution. Also, due to noise and vibration caused by the impacts, operators are fatigued mentally and physically and there is a risk of their being attacked by Steinbrocken syndrome or by Raynaud's phenomenon. In fact, this is becoming an object of public concern.
Under the above circumstances, as a method of obtaining impulse torque, a torque wrench which prevents noise and vibration by utilizing oil pressure is considered promising. Such a torque wrench generates a constant torque and has such advantages as stabilization of tightening torque and much less noise and vibration, because of the use of oil pressure pulses instead of impacts by a mechanical method. Therefore, torque wrenches of this type are adopted widely by users. This type of torque wrench has an oil pressure impulse torque generator with a single blade or plural blades provided on a main shaft. For example, such a torque wrench with four blades is disclosed in U.S. Pat. No. 3,263,449 (Aug. 2, 1966). In the case of the former using a single blade, oil pressure of the impulse torque generator becomes higher, for which a more precise and stronger sealing construction is required. In addition, pressure is given to the blade only at one side in the circumferential direction of the main shaft and the resultant inclination of the main shaft causes such trouble as loss of output, irregularity of torque, seizing of machine parts, etc. In the case of the latter using four blades, as impulse is generated at least twice upon each rotation of the liner, the inertia of rotating mass of the liner and the liner casing is therefore less, and consequently, the impulse torque becomes lower.